LongevityJanuary 2, 2026·5 min read
By the CIRRUS Editorial Team — how we write and source this
Biological age tests: how they work and their limits
A test claims to tell you your body is younger or older than your birth certificate. Here's what's actually being measured.
Most commercial biological age tests rely on DNA methylation patterns — chemical modifications to DNA that change in fairly predictable patterns with age — using an algorithm (an "epigenetic clock") trained on large datasets to estimate biological age from these patterns in a blood or saliva sample.
The underlying science is genuinely active and legitimate research territory, with several different epigenetic clock algorithms developed by different research groups, each trained somewhat differently and showing meaningfully different results when applied to the same sample.
This inter-algorithm variability is the core practical limitation: different biological age tests can give a meaningfully different number for the same person, which makes a single test's absolute number less reliable than tracking the same specific test's trend over time in the same individual.
As with several items on this list, the research direction is promising and worth continued attention, but the current commercial products should be treated as an emerging, imperfect estimate rather than a precise, validated measurement of true biological aging.
This article is general health information, not medical advice, and doesn’t replace evaluation by your own physician. Talk to a doctor about anything specific to your own diagnosis or treatment.